JP7538005B2 - Steering system - Google Patents

Description

The present invention relates to a steer-by-wire type steering system installed in a vehicle.

Recently, a steering system in which the steering operation member such as a steering wheel is not mechanically connected to the wheels, and the wheels are steered by a steering actuator having an electric motor without relying on the operating force of the driver, that is, a steer-by-wire type steering system, has been considered. Steer-by-wire type steering systems generally employ a reaction force imparting mechanism for imparting an operating reaction force to the steering operation member to give the driver a feeling of operation. In the steer-by-wire type steering system described in the following patent document, when a specific phenomenon occurs, control is executed to increase the operating reaction force by the reaction force imparting mechanism in order to limit the operation of the steering operation member, taking into account the load on the steering actuator.

JP 2020-83059 A

In the steering system described in the above patent document, the steering control by the steering actuator and the control of the operation reaction force by the reaction force applying mechanism are performed by one controller, but for reasons such as simplifying the system and improving versatility, it is also considered to perform these controls separately by two controllers. When executing the above control to increase the operation reaction force in a system employing two controllers, information on various parameters related to the steering actuator, i.e., the steering speed of the wheels, the current supplied to the electric motor, the temperature of the electric motor, the voltage introduced from the battery, etc., must be transmitted from the controller that controls the steering to the controller that controls the operation reaction force as the state of the steering device with respect to the above specific phenomenon. Since this increases the communication burden of the system, reducing this burden leads to improved practicality of a steer-by-wire type steering system composed of two controllers. The present invention was made in consideration of such actual circumstances, and its objective is to provide a highly practical steer-by-wire type steering system.

In order to solve the above problems, the steering system of the present invention comprises:
an operation device including a steering operation member operated by a driver, a reaction force imparting mechanism that imparts an operation reaction force to the steering operation member by a reaction force motor, and an operation controller that controls the operation reaction force;
A steering device including a steering actuator that steers wheels by a steering motor and a steering controller that controls an amount of steering of the wheels by the steering actuator;
a communication line that communicably connects the operation controller and the steering controller, the steer-by-wire type steering system being mounted on a vehicle,
The operation controller:
a basic reaction force control that changes an operation reaction force based on an operation amount of the steering operation member, a traveling speed of the vehicle, and an operation force applied to the steering operation member;
a reaction force changing process for changing a magnitude of an operation reaction force according to a state of the steering device;
Run
The steering controller is configured to determine a status code based on a status of the steering device and transmit the status code to the operation controller via the communication line, and the operation controller executes the reaction force change processing in accordance with the received status code.

According to the present invention, simply by transmitting a code indicating the state of the steering device from the steering controller to the operation controller, the operation controller that receives the code can execute a process for changing the magnitude of the operation reaction force (hereinafter sometimes referred to as "reaction force change process") based on the code. This makes the steering system a system with a low communication burden.

Aspects of the invention

The operation reaction force generally changes according to the amount of operation of the steering operation member (hereinafter sometimes simply referred to as the "operation member") and can also be changed based on, for example, the vehicle's traveling speed (hereinafter sometimes abbreviated to "vehicle speed") or the operating force applied to the operation member. The change in operation reaction force realized by the reaction force change process according to the present invention is different from such a change in operation reaction force or is at a different level, and in short, means a change according to the state of the steering device. Therefore, the change according to the amount of operation, etc. and the change in operation reaction force realized by the reaction force change process may be performed simultaneously.

The "condition code" may be categorized according to the phenomenon occurring in the steering device, for example. Specifically, for example, the condition code may be categorized according to the phenomenon of overheating of the steering device, i.e., the steering motor, the phenomenon of a voltage drop introduced from the power source to the driver (drive circuit such as an inverter) of the steering motor, the phenomenon of steering of the wheels being hindered by a steering barrier such as a ditch or curb, etc. Simply put, the condition code may be categorized according to the type of phenomenon.

When the status codes are categorized, the status codes may be ranked according to the type of phenomenon and the severity of the phenomenon (temperature of the steering motor, voltage level, degree of steering obstruction due to a steering barrier, etc.). In more detail, the status codes may be ordered in terms of, for example, the degree of need for action, urgency, importance, etc. In other words, a priority may be set for the status codes.

It is possible that multiple different types of phenomena may occur. In that case, if a hierarchy is established for the status codes, it is desirable for the steering controller to transmit a status code with a higher hierarchy, for example. By transmitting a single status code rather than multiple status codes, it is possible to execute the reaction force change process simply and appropriately. When the status code transmitted by the steering controller is changed so as to raise the hierarchy, the operation controller can execute the reaction force change process so as to add the amount of change in the operation reaction force based on the status code after the change to the amount of change in the operation reaction force based on the status code before the change. This reaction force change process makes it possible to avoid a situation in which the operation reaction force becomes smaller despite a higher hierarchy.

1 is a diagram showing a schematic diagram of an overall configuration of a steering system according to an embodiment of the present invention; 10 is a graph showing an assist-dependent decrease component, which is one component of an operation reaction force, in relation to an operation torque applied to a steering operation member. 4 is a flowchart of an operation program executed in the steering system of the embodiment. 4 is a flowchart of a steering program executed in the steering system of the embodiment. 6 is a flowchart of a state identification processing subroutine constituting a steering program. 13 is a flowchart of an operation reaction force determination process subroutine that constitutes the operation program. 11 is a flowchart of a normal processing subroutine and a first type processing subroutine, which constitute the actuation reaction force determination processing subroutine. 13 is a flowchart of a second type processing subroutine constituting the actuation reaction force determination processing subroutine. 13 is a flowchart of a third type processing subroutine constituting the actuation reaction force determination processing subroutine.

Below, as a form for carrying out the present invention, a steering system which is an embodiment of the present invention will be described in detail with reference to the drawings. In addition to the following embodiment, the present invention can be carried out in various forms including the form described in the above [Modes of the invention] section, with various modifications and improvements made based on the knowledge of those skilled in the art.

[A] Hardware Configuration of the Steering System The steering system of the embodiment mounted on a vehicle is a system for steering two wheels 10, each of which is a steerable wheel, as shown diagrammatically in FIG. 1, and is a steer-by-wire type steering system equipped with an operating device 12 and a steering device 14 which are mechanically independent of each other.

The operation device 12 includes a) a steering wheel 20 as a steering operation member steered by the driver, b) a steering shaft 22 to the tip of which the steering wheel 20 is attached, c) a steering column 24 that rotatably holds the steering shaft 22 and is supported by an instrument panel reinforcement (not shown), and d) a reaction force imparting mechanism 28 that uses a reaction force motor 26, which is an electric motor supported by the steering column 24, as a power source to impart a reaction force (strictly speaking, a reaction torque, but hereinafter, the commonly used term "operation reaction force") _FCT against the steering operation to the steering wheel 20 via the steering shaft 22. This reaction force imparting mechanism 28 has a general structure including a reducer and the like, and therefore a description of the specific structure of the reaction force imparting mechanism 28 will be omitted.

The operation device 12 has an operation angle sensor 30 that detects the operation angle δ of the steering wheel 20 as the steering operation amount. When the steering wheel 20 is in a neutral position while the vehicle is traveling straight ahead, the rotation angle from the neutral position is the operation angle δ of the steering wheel 20. A torsion bar 32 is incorporated in the steering shaft 22, and an operation torque sensor 34 is provided to detect the operation torque Tq as the operation force applied to the steering wheel 20 by the driver based on the amount of twist of the torsion bar 32.

Each of the wheels 10 is supported on the vehicle body so that it can be turned via the steering knuckle 40. The steering device 14 turns each of the wheels 10 as a unit by rotating the steering knuckle 40. The steering device 14 has a steering actuator 42 as a main component. The steering actuator 42 is composed of a) a steering rod 46 whose both ends are connected to the left and right steering knuckles 40 via link rods 44, b) a housing 48 that supports the steering rod 46 so that it can move left and right and is fixedly held on the vehicle body, and c) a rod moving mechanism 52 that uses the steering motor 50, which is an electric motor, as a driving source to move the steering rod 46 left and right. The rod moving mechanism 52 is mainly composed of a ball screw mechanism composed of a ball groove screwed into the steering rod 46 and a nut that is screwed into the ball groove via a bearing ball and is rotated by the steering motor 50, and has a general structure, so a detailed explanation of the rod moving mechanism 52 will be omitted here.

The steering device 14 has a steering angle sensor 54 for detecting the amount of movement of the steering rod 46 from a neutral position (the position where the vehicle is located when traveling straight ahead) to detect the steering angle θ as the amount of steering of the wheels 10. In addition, the housing 48 of the steering actuator 42 is provided with a temperature sensor 56 for detecting the temperature of the area near the steering motor 50 (hereinafter, for convenience, may be referred to as the "motor temperature").

Control of the operation device 12, more specifically, control of the operation reaction force _FCT , i.e., control of the reaction motor 26 of the operation device 12, is executed by an operation electronic control unit (hereinafter sometimes referred to as an "operation ECU") 60 serving as an operation controller that is a controller of the operation device 12. The operation ECU 60 is composed of a computer having a CPU, ROM, RAM, etc., a driver for the reaction motor 26 (specifically, an inverter, since the reaction motor 26 is a three-phase brushless motor), etc.

Similarly, the control of the steering device 14, more specifically, the control of the steering angle θ, i.e., the control of the steering motor 50 of the steering device 14, is executed by a steering electronic control unit (hereinafter sometimes referred to as the "steering ECU") 62, which serves as a steering controller that is a controller of the steering device 14. The steering ECU 62 is composed of a computer having a CPU, ROM, RAM, etc., and a driver for the steering motor 50 (specifically, an inverter, since the steering motor 50 is a three-phase brushless motor). The steering ECU 62 has a voltage sensor 64 for detecting the voltage (hereinafter sometimes referred to as the "introduced voltage") V introduced from the battery to the steering ECU 62 in order to supply current to the steering motor 50, or, simply put, the battery voltage V.

As will be explained in detail later, the operation ECU 60 and the steering ECU 62 execute control processing while transmitting and receiving information to each other. For this reason, the operation ECU 60 and the steering ECU 62 are connected to a CAN (car area network or controllable area network) 66, which serves as a communication line.

[B] Control of the Steering System The steering system of the embodiment, like a general steer-by-wire type steering system, executes wheel steering control in response to a steering operation (hereinafter sometimes simply referred to as "steering control") and control of the operation reaction force (hereinafter sometimes simply referred to as "reaction force control"). However, the steering system of the embodiment also executes a process for changing the magnitude of the operation reaction force in response to the state of the steering device 14 (hereinafter sometimes referred to as "reaction force change process"). Below, the steering control, basic reaction force control which is a basic reaction force control, and reaction force change process will be explained in order, and then the flow of these controls will be briefly explained.

(a) Steering control Steering control is control for realizing steering of the wheels 10 in response to a steering operation of the steering wheel 20. The operation ECU 60 detects the operation angle δ of the steering wheel 20 via the operation angle sensor 30, and determines a target steering angle θ ^* that is a target for the steering angle θ of the wheels 10 by multiplying the detected operation angle δ by a set steering gear ratio _RG according to the following equation.
θ ^* ＝ _RG ×δ
The operation ECU 60 transmits information relating to the determined target steering angle θ ^* to the steering ECU 62 via the CAN 66 .

The steering ECU 62 receives information related to the target steering angle θ ^* , and detects the actual steering angle θ of the wheels 10 (hereinafter sometimes referred to as "actual steering angle θ") via the steering angle sensor 54. The steering ECU 62 determines a steering angle deviation Δθ, which is the deviation of the actual steering angle θ from the target steering angle θ ^* , in accordance with the following equation.
Δθ＝θ ^* -θ
Then, steering ECU 62 determines current _IS to be supplied to steering motor 50 in accordance with a feedback control law based on steering angle deviation Δθ, that is, in accordance with the following equation: The first, second and third terms in the following equation are a proportional term, an integral term and a differential term, respectively, and G _P , G _I and G _D are a proportional term gain, an integral term gain and a differential term gain, respectively.
I _S =G _P ×Δθ+G _I ×∫Δθdt+G _D ×dΔθ/dt
The steering ECU 62 supplies the determined current I _S to the steering motor 50 .

(b) Basic Reaction Force Control The reaction force control is a control for giving the driver a feeling of operation in response to the steering operation. In the basic reaction force control, the operation ECU 60 determines the operation reaction force F _CT based on two components, a steering force-dependent component F _S and an assist-dependent reduction component F _A , in accordance with the following formula.
_FCT = Fs _{- F}

The steering force dependent component F _S is a component related to the steering force required to steer the wheels 10, and is determined according to the following equation.
F _S = f _SA (δ, v) + f _F (dδ, v)

The first term f _SA (δ, v) in the above equation is a self-aligning-dependent function whose parameters are the operation angle δ of the steering wheel 20 and the vehicle traveling speed (hereinafter sometimes abbreviated as "vehicle speed") v, and can be considered as a component based on the self-aligning torque acting on the wheels 10. According to the self-aligning-dependent function f _SA (δ, v), the steering force-dependent component F _S is determined to be larger the higher the vehicle speed v and the larger the operation angle δ.

The second term _fF (dδ,v) in the above formula is a road-friction-dependent function with parameters being the operation speed dδ, which is the rate of change of the operation angle δ, and the vehicle speed v, and can be considered as a component based on the force acting on the wheels 10 due to friction of the road surface. According to the road-friction-dependent function _fF (dδ,v), for example, taking into account so-called stationary steering, the steering force-dependent component _Fs is determined to be larger as the vehicle speed v becomes lower and larger as the operation speed dδ becomes higher.

Since the determination of the above-mentioned steering force dependent component F _S in the basic reaction force control is an already known technique, a detailed description thereof will be omitted here. The vehicle speed v is determined by a brake ECU (not shown), which is an electronic control unit of the brake system, based on the wheel rotation speed detected by a wheel speed sensor provided on the wheel 10. The brake ECU is also connected to the CAN 66, and the operation ECU 60 obtains the vehicle speed v based on information transmitted from the brake ECU via the CAN 66. The operation ECU 60 also specifies the operation speed d δ based on the change in the detected operation angle δ.

The assist-dependent reduction component F _A can be considered as a component for providing the driver with a so-called power steering operation feeling. In power steering, an assist torque corresponding to the operation torque Tq is generally applied to the steering shaft 22. The assist-dependent reduction component F _A is determined according to the following equation so as to simulate the assist torque.
_F = _fT (Tq)
_fT (Tq) is an assist function with the operation torque Tq as a parameter, and according to this assist function, the assist-dependent decrease component is determined to be larger as the operation torque Tq increases. Schematically, it is determined based on the operation torque Tq as shown in the graph of FIG. 2(a).

The determination of the above-mentioned steering force dependent component F _S in the basic reaction force control is an already known technique, and therefore a detailed description thereof will be omitted here. The operation ECU 60 detects the operation torque Tq via the operation torque sensor 34.

Based on the actuation reaction force _FCT determined as described above, the operation ECU 60 determines the current I _C to be supplied to the reaction force motor 26 in accordance with the following equation, and supplies the determined current I _C to the reaction force motor 26. Note that α in the following equation is a current determination coefficient that has been set.
I _C =α×F _CT

According to the basic reaction force control as described above, the operation reaction force F _CT can be appropriately controlled without receiving information from the steering device 14 via CAN 66, and control with a small communication burden between the operation device 12 and the steering device 14 is realized.
(c) Reaction force change processing
i) Significance of reaction force change processing In a steer-by-wire type steering system, the operation reaction force F _CT plays a role of giving the driver an appropriate operation feeling, but it is also possible to have another role. More specifically, for example, when the steering actuator 42, particularly the steering motor 50, overheats, it is desired to limit the output of the steering motor 50, that is, to limit the steering of the wheels 10, in order to protect the steering motor 50. Also, when the voltage of the battery, which is the power source for supplying current to the steering motor 50, that is, the voltage V introduced into the steering ECU 62 (hereinafter sometimes referred to as the "introduced voltage") drops, it is also desired to limit the steering of the wheels 10 in order to reduce the burden on the steering actuator 42. Furthermore, when the steering of the wheels 10 is hindered by a barrier such as a curb or a groove, it is necessary to make the driver aware of the presence of the barrier. In order to recognize such a steering restriction and a steering barrier, it is possible to change the magnitude of the operation reaction force F _CT from the magnitude generated in the basic reaction force control, more specifically, to make it larger. In other words, the reaction force change process can give the operation reaction force FCT the role of imposing steering restrictions on the driver based on the state of the steering device 14, or the role of making the driver aware of steering barriers based on the state of the _steering device 14.

ii) Communication burden The reaction force change processing that has been considered so far has been performed based on the motor temperature T, the introduction voltage V, the steering speed dθ, which is the rate of change of the steering angle θ, the supply current I _S to the steering motor 50, and the like, which are respectively detected for the steering motor 50. When such a reaction force change processing is executed in the steering system of the embodiment, it is generally considered that the detection of the motor temperature T, the introduction voltage V, the steering speed dθ, and the supply current I _S is performed by the steering ECU 62, while the reaction force change processing is performed by the operation ECU 60. In other words, information related to the detected motor temperature T, the introduction voltage V, the steering speed dθ, and the supply current I _S must be transmitted from the steering ECU 62 to the operation ECU 60 via the communication line CAN 66 at all times. Such a large amount of information transmission and reception is a communication burden in the system. This burden may eventually cause a delay in the control of the steering system, or may cause a failure in the control of other systems connected to the CAN 66.

iii) Coding of steering device state In consideration of the above-mentioned communication burden, in the steering system of this embodiment, the steering ECU 62 codes the state of the steering device 14 based on the motor temperature T, the input voltage V, the steering speed dθ, and the supply current I _S , and transmits one state code to the operation ECU 60 via CAN 66. The operation ECU 60 changes the operation reaction force F _CT in accordance with preset rules, based on the transmitted state code.

The status codes are as shown in the table below, and are categorized according to the phenomenon occurring in the steering device 14, and are ranked based on the type of the phenomenon and the severity of the phenomenon (which can also be considered as the severity of symptoms). In other words, the codes are ranked from the perspective of the degree of necessity to deal with the phenomenon, the urgency of the deal, and the importance of the deal.

The types of phenomena that are targeted are an overheated state where the motor temperature T is high (Type 1), a low voltage state where the introduction voltage V is low (Type 2), and a barrier presence state where a steering barrier is present (Type 3), and the normal state is when the phenomena that are targeted are not occurring. The status codes are "0" for the normal state, "1*" for an overheated state, "2*" for a low voltage state, and "3*" for a barrier presence state (* indicates some degree). In the status codes, the severity of the phenomenon is indicated as "*L" for mild, "*M" for medium, and "*H" for severe (* indicates some degree).

The status codes are set so that the order increases as you go down the table. Specifically, from lowest to highest, there are nine status codes: normal status "0", mild overheated status "1L", moderate overheated status "1M", severe overheated status "1H", mild low voltage status "2L", moderate low voltage status "2M", severe low voltage status "2M", mild barrier present status "3L", and severe barrier present status "3H".

The steering ECU 62 specifies the current state of the steering device 14 based on the motor temperature T, the introduced voltage V, the steering speed dθ, and the supply current I _S , and determines a state code. Specifically, when the motor temperature T detected via the temperature sensor 56 is higher than the mild threshold temperature T _L and equal to or lower than the moderate threshold temperature T _M , the state code is determined to be a mild overheated state "1L", when the motor temperature T detected via the temperature sensor 56 is higher than the moderate threshold temperature T _M and equal to or lower than the severe threshold temperature T _H , the state code is determined to be a moderate overheated state "1M", and when the motor temperature T is higher than the severe threshold temperature T _H , the state code is determined to be a severe overheated state "1H". Also, when the introduced voltage V detected via the voltage sensor 64 is lower than the mild threshold voltage V _L and equal to or higher than the moderate threshold voltage V _M , the state code is determined to be a mild low voltage state "2L", when the introduced voltage V is lower than the moderate threshold voltage V _M and equal to or higher than the severe threshold voltage V _H , the state code is determined to be a moderate low voltage state "2M", and when the introduced voltage V is lower than the severe threshold voltage V _H , the state code is determined to be a severe low voltage state "2H". Furthermore, when the steering speed dθ is lower than the threshold speed dθ _TH , that is, when the steering angle θ is considered to have not substantially changed, if the supply current I _S to the steering motor 50 is greater than the mild threshold current I _SL and equal to or less than the severe threshold current I _SH , the state code is set to a mild barrier presence state "3L", and if the supply current I S is greater than the severe threshold current I _SH , the state code is set to a severe barrier presence state "3H".

It is possible that the steering device 14 may be in a state where two or more status codes are determined. However, from the perspective of reducing the communication burden, even when two or more status codes are determined, the steering ECU 62 determines only the status code with the higher rank, in other words, the status code with the highest rank, as the current status code, and transmits information about that one status code to the operation ECU 60. Note that hereinafter, the transmission and reception of information about status codes may sometimes be simply referred to as the transmission and reception of status codes.

iv) Changing the actuation reaction force based on the state code Simply put, the operation ECU 60 changes the actuation reaction force _FCT by the basic reaction force control in accordance with the state code. In other words, the actuation reaction force _FCT is determined so that the actuation reaction force _FCT that would be determined by the basic reaction force control is shifted by an amount corresponding to the state code.

More specifically, when the received state code is a code indicating an overheated state, the operation ECU 60 increases the actuation reaction force F _CT by decreasing the assist-dependent decrease component F _A in the basic reaction force control as the first type processing. As described above, in the normal state, the assist-dependent decrease component F _A is determined according to the assist function f _T (Tq) as shown in FIG. 2(a). In contrast, in the overheated state, the operation ECU 60 determines the assist-dependent decrease component F A according to the assist function f _T (Tq-ΔTq) as shown in _FIG . 2(b), which has as a parameter the operation torque Tq reduced by the reduction torque ΔTq. By reducing the parameter operation torque Tq, the assist-dependent decrease component F _A is reduced, and as a result, the actuation reaction force F _CT increases. More specifically, the reduction torque ΔTq is determined to a different value depending on the degree of the overheated state. Specifically, the operation ECU 60 determines the reduction torque ΔTq to be the mild torque _ΔTqL when the mild overheat state is "1L", to be the moderate torque ΔTqM larger than the mild torque _ΔTqL when the moderate overheat state is "1M", and to be the severe torque _ΔTqH larger than the moderate torque _ΔTqM when the severe overheat state is " _1H ". In other words, the higher the degree, the more the assist-dependent reduction component _FA is reduced, and the more the operation reaction force _FCT is increased.

If the received status code is a code indicating a low voltage state, the operation ECU 60 increases the actuation reaction force F _CT by setting an upper limit on the assist-dependent decrease component F _A in the basic reaction force control as the second type processing. In detail, as shown in FIG. 2C, when the assist-dependent decrease component F _A determined in the basic reaction force control exceeds the upper limit value F _AL , the operation ECU 60 determines the assist-dependent decrease component F _A to be the upper limit value F _AL . By imposing such a limit on the assist-dependent decrease component F _A , the assist-dependent decrease component F _A is reduced within the range in which the limit is imposed, and as a result, the actuation reaction force F _CT increases. Moreover, the upper limit value F _AL is determined to a different value depending on the degree of the low voltage state. Specifically, the operation ECU 60 sets the upper limit value F _AL to a mild value F _ALL when the state is a mild low-voltage state "2L", to a moderate value F _ALM smaller than the mild value F _ALL when the state is a moderate low-voltage state "2M", and to a severe value F _ALH smaller than the moderate value F _ALM when the state is a severe low-voltage state "2H". In other words, the higher the state is, the more the assist-dependent decrease component F _A is restricted, and the more the operation reaction force F _CT is increased in accordance with the restriction.

If the received status code indicates a barrier presence state, the operation ECU 60 performs the third type process by increasing the actuation reaction force F _CT in the basic reaction force control by adding a barrier-dependent component F _B to the actuation reaction force F _CT . That is, the actuation reaction force F _CT is determined according to the following formula:
F _CT = F _S - F _A + F _B
The barrier-dependent component F _B is determined to a different value depending on the degree of the barrier presence state. Specifically, the operation ECU 60 determines the barrier-dependent component F _B to be the mild component F _BL when the barrier presence state is "3L", and to be the severe component F _BH larger than the mild component F _BL when the barrier presence state is "3H". In other words, the higher the degree, the larger the barrier-dependent component F _B is added, thereby increasing the operation reaction force F _CT .

As explained above, there are cases where the steering device 14 is in two or more different states, and even in such cases, only one state code with a higher rank is transmitted from the steering ECU 62 to the operation ECU 60. Therefore, even if the transmitted state code changes to one with a higher rank, it is possible that the operation reaction force _FCT will decrease.

Therefore, in this steering system, when the state code is changed to one with a different type of phenomenon, and the change is such that the order is raised, a measure is taken so that the actuation reaction force _FCT is not reduced. To explain in detail, the operation ECU 60 stores the values of the reduction torque ΔTq and the upper limit value _FAL for determining the assist-dependent reduction component F _A as the previous value _ΔTqPR and the previous value _FALPR , and when the state code is changed from the overheat state "1*" to the low voltage state "2*" or the barrier existence state "3*", the reduction torque ΔTq is maintained at the previous value _ΔTqPR , and when the state code is changed from the low voltage state "2*" to the barrier existence state "3*", the upper limit value _FAL is maintained at the previous value _FALPR . This prevents the actuation reaction force _FCT from being reduced when the order is raised.

[C] Control flow of the steering system In this steering system, the above-mentioned steering control, basic reaction force control, and reaction force change processing are performed by the operation ECU 60 repeatedly executing the operation program shown in the flowchart of Fig. 3, and the steering ECU 62 repeatedly executing the steering program shown in the flowchart of Fig. 4, at short time intervals (for example, several meters to several tens of milliseconds). Below, the processing according to these programs will be explained to briefly explain the control flow of this steering system, i.e., the flow of the steering control, basic reaction force control, and reaction force change processing.

In the process according to the operation program, first, in step 1 (hereinafter abbreviated as "S1"; the same applies to the other steps), the operation angle δ of the steering wheel 20 is detected via the operation angle sensor 30. In the next step S2, the detected operation angle δ is multiplied by a predetermined steering gear ratio R _G to determine a target steering angle θ ^* , and in step S3, information on the target steering angle θ ^* is transmitted to the steering ECU 62.

In the next step S4, a process for determining the actuation reaction force F _CT (hereinafter sometimes referred to as "actuation reaction force determination process") is executed. The details of this process will be described later. After the actuation reaction force determination process, in step S5, the determined actuation reaction force F _CT is multiplied by a predetermined current determination coefficient α to determine a supply current I _C to the reaction force motor 26, and in step S6, the current I _C is supplied to the reaction force motor 26.

In the processing according to the steering program, first, in S11, information on target steering angle θ ^* transmitted from operation ECU 60 is received. In the following S12, actual steering angle θ, which is the steering angle of actual wheels 10, is detected via steering angle sensor 54, and in S13, the detected actual steering angle θ is subtracted from the received target steering angle θ ^* to determine steering angle deviation Δθ. Then, in S14, supply current I _S to steering motor 50 is determined by a method in accordance with the feedback control law based on the steering angle deviation Δθ explained above, and in S15, the current I _S is supplied to steering motor 50.

In the next step S16, a state identification process is executed to identify the state of the steering device 14. This state identification process is performed by executing a state identification process subroutine whose flowchart is shown in FIG. 5.

In the processing according to the condition identification processing subroutine, first, in S21, motor temperature T, which is the temperature in the vicinity of steering motor 50, is detected via temperature sensor 56. In subsequent S22 to S24, the detected motor temperature T is compared with mild threshold temperature T _L , medium threshold temperature T _M and severe threshold temperature T _H , and in S25 to S28, if motor temperature T is higher than severe threshold temperature T _H , the condition code is set to "1H", if motor temperature T is higher than medium threshold temperature T _M and equal to or lower than severe threshold temperature T _H , the condition code is set to "1M", if motor temperature T is higher than mild threshold temperature T _L and equal to or lower than medium threshold temperature T _M , the condition code is set to "1L", and if motor temperature T is equal to or lower than mild threshold temperature T _L , the condition code is set to "0".

Next, in S29, the introduction voltage V, which is the voltage of the battery introduced into the steering ECU 62, is detected via the voltage sensor 64. In the following S30 to S32, the detected introduction voltage V is compared with the mild threshold voltage _VL , the medium threshold voltage _VM , and the severe threshold temperature _VH , and in S33 to S36, if the introduction voltage V is lower than the severe threshold voltage _VH , the status code is replaced with "2H", if the introduction voltage V is lower than the medium threshold voltage _VM and equal to or higher than the severe threshold temperature _VH , the status code is replaced with "2M", if the introduction voltage V is lower than the mild threshold voltage _VL and equal to or higher than the medium threshold voltage _VM , the status code is replaced with "2L", and if the introduction voltage V is equal to or higher than the mild threshold voltage _VL , the already determined status code is maintained.

Next, in S37, the steering speed dθ is specified based on the change in the actual steering angle θ, and it is determined whether the steering speed dθ is lower than the threshold speed dθ _TH , in other words, whether the wheels 10 are substantially being steered. If the steering speed dθ is lower than the threshold speed dθ _TH , in S38 and S39, the determined supply current I _S to the steering motor 50 is compared with the mild threshold current I _SL and the severe threshold current I _SH , and in S40 to S42, if the supply current I _S is larger than the severe threshold current I _SH , the status code is replaced with "3H", if the supply current I _S is larger than the mild threshold current I _SL and equal to or less than the severe threshold current I _SH , the status code is replaced with "3L", and if the supply current I _S is equal to or less than the mild threshold current I _SL , the already determined status code is maintained. Incidentally, even if it is determined in S37 that the steering speed dθ is equal to or greater than the threshold speed dθ _TH , the already determined state code code is maintained in S42.

The status code determined in the above manner will be the highest ranked one even if multiple phenomena occur, and information about that status code will be sent to the operation ECU 60 in S43.

The operation reaction force determination process of S4 of the operation program is performed by executing an operation reaction force determination process subroutine shown in the flowchart of Fig. 6. In the process according to this subroutine, first, in S51, the vehicle speed v of the vehicle is determined based on information sent from the brake ECU. In the following S52, as described above, the steering force dependent component F _S is determined using the self-aligning dependent function f _SA (δ,v) and the road surface friction dependent function f _F (dδ,v). Next, in S53, the operation torque Tq is detected via the operation torque sensor 34.

The following steps S54 to S57 are processes according to the state code code sent from the steering ECU 62. The normal process of S54 is performed by executing a normal process subroutine whose flow chart is shown in FIG. 7. In the process according to this subroutine, first, in S541, it is determined whether or not the sent state code code is "0". If the state code code is "0", in S542, the above-mentioned reduction torque ΔTq is set to 0, the upper limit of the above-mentioned assist-dependent reduction component F _A is released (in the flow chart, it is expressed that the upper limit value F _AL of the assist-dependent reduction component F _A is set to ∞), and further, the above-mentioned barrier-dependent component F _B is determined to be 0. Then, in S543, the maintenance flag FL, which will be described in detail later, is reset to "0". Note that, if it is determined in S541 that the state code code is not "0", S542 and S543 are skipped.

The first type processing in S55 is performed by executing a first type processing subroutine whose flow chart is shown in FIG. 7. In the processing according to this subroutine, first, in S551, it is determined whether the transmitted status code is any one of "1L", "1M", and "1H", that is, whether it is a code indicating an overheated state. If the status code is any one of "1L", "1M", and "1H", in S552, as described above, the reduced torque ΔT is determined according to the degree of the overheated state, specifically, in the case of a mild overheated state, it is set to a mild torque ΔTq _L , in the case of a medium overheated state, it is set to a medium torque ΔTq _M , and in the case of a heavy overheated state, it is set to a heavy torque ΔTq _H. Then, in S553, the upper limit of the above-mentioned assist-dependent reduced component F _A is released, and the barrier-dependent component F _B is set to 0. Note that, if it is determined in S551 that the status code does not indicate an overheated state, S552 and S553 are skipped.

The second type processing in S56 is performed by executing a second type processing subroutine whose flow chart is shown in Fig. 8. In the processing according to this subroutine, first, in S561, it is determined whether the transmitted status code is any of "2L", "2M", and "2H", that is, whether it is a code indicating a low voltage state. If the status code is any of "2L", "2M", and "2H", it is determined in S562 whether the status code has been changed to a higher rank in the current processing, that is, whether the status code has changed from one indicating an overheat state to one indicating a low voltage state. If the status code has changed from one indicating an overheat state to one indicating a low voltage state, in S563, the maintenance flag FL is set to "1". The maintenance flag FL is initially set to "0" and is set to "1" when the reduction torque ΔTq or both the reduction torque ΔTq and the upper limit value F _AL of the assist-dependent reduction component _FA should inherit the values from the previous execution of the program, i.e., the previous value ΔTq _PR and the previous value F _ALPR . If the status code has not changed this time from one indicating an overheat state to one indicating a low voltage state, S563 is skipped.

In the next S564, it is determined whether the maintenance flag FL is "1". If the maintenance flag FL is "1", in S565, the reduction torque ΔTq is set to the previous value ΔTq _PR . If the maintenance flag FL is "0", in S566, the reduction torque ΔTq is set to 0. In the next S567, as described above, the upper limit value F _AL of the assist-dependent reduction component F _A is determined according to the degree of the low voltage state, specifically, in the case of a low voltage state, to a low voltage value F _ALL , in the case of a medium voltage state, to a medium voltage value F _ALM , and in the case of a heavy voltage state, to a heavy voltage value F _ALH . Then, in S568, the barrier-dependent component F _B is determined to 0. Note that, if it is determined in S561 that the state code code does not indicate a low voltage state, the steps from S562 onwards are skipped.

The third type processing of S57 is performed by executing a third type processing subroutine whose flow chart is shown in FIG. 9. In the processing according to this subroutine, first, in S571, it is determined whether the transmitted status code is either "3L" or "3H", that is, whether it is a code indicating a barrier presence state. If the status code is either "3L" or "3H", it is determined in S572 whether the status code has been changed to a higher rank in the current processing, that is, whether the status code has changed from one indicating an overheat state or a low voltage state to one indicating a barrier presence state. If the status code has changed from one indicating an overheat state or a low voltage state to one indicating a barrier presence state, in S573, the maintenance flag FL is set to "1". If the status code has not changed from one indicating an overheat state or a low voltage state to one indicating a barrier presence state, S573 is skipped.

In the next S574, it is determined whether the maintenance flag FL is "1" or not. If the maintenance flag FL is "1", in S575, the reduction torque ΔTq and the upper limit value F _AL of the assist-dependent reduction component F _A are set to the previous value ΔTq _PR and the previous value F _ALPR , respectively. If the maintenance flag FL is "0", in S576, the reduction torque ΔTq is set to 0, and the upper limit of the assist-dependent reduction component F _A is released. In the next S577, as described above, the barrier-dependent component F _B is determined according to the degree of the barrier presence state, specifically, in the case of a mild barrier presence state, to the mild component F _BL , and in the case of a severe barrier presence state, to the severe component F _BH . Note that, if it is determined in S571 that the state code code does not indicate a barrier presence state, the steps from S572 onwards are skipped.

6, after the third type process in S57, the assist-dependent decrease component F _A is determined in S58 using the assist function f _T (Tq-ΔTq) as described above. In the following S59, it is determined whether the determined assist-dependent decrease component F _A is larger than the upper limit value F _AL , and if it is larger, in S60, the assist-dependent decrease component F _A is set to the upper limit value F _AL .

Then, in S61, the actuation reaction force F _CT is determined by subtracting the assist-dependent reduction component F _A from the steering force-dependent component F _S and adding the barrier-dependent component F _B to the result, and in S62, the currently determined reduction torque ΔTq and upper limit value F _AL of the assist-dependent reduction component F _A are stored as the previous value ΔTq _PR and the previous value F _ALPR , respectively, for the next execution of the program.

10: Wheels 12: Operation device 14: Steering device 20: Steering wheel (steering operation member) 26: Reaction motor 28: Reaction mechanism 42: Steering actuator 50: Steering motor 60: Operation electronic control unit (operation ECU) (operation controller) 62: Steering electronic control unit (steering ECU) (steering controller) 66: CAN (communication line)

Claims (6)

an operation device including a steering operation member operated by a driver, a reaction force imparting mechanism that imparts an operation reaction force to the steering operation member by a reaction force motor, and an operation controller that controls the operation reaction force;
A steering device including a steering actuator that steers wheels by a steering motor and a steering controller that controls an amount of steering of the wheels by the steering actuator;
a communication line that communicably connects the operation controller and the steering controller, the steer-by-wire type steering system being mounted on a vehicle,
The operation controller:
a basic reaction force control that changes an operation reaction force based on an operation amount of the steering operation member, a traveling speed of the vehicle, and an operation force applied to the steering operation member;
a reaction force changing process for changing a magnitude of an operation reaction force according to a state of the steering device;
Run
The steering controller determines a status code based on a status of the steering device and transmits the status code to the operation controller via the communication line, and the operation controller executes the reaction force change process in accordance with the received status code. 2. The steering system according to claim 1, wherein the condition codes are categorized according to phenomena occurring in the steering device. The status code is
3. The steering system according to claim 2, wherein each of the above-mentioned phenomena is categorized according to the overheating phenomenon of the steering motor, the phenomenon of a voltage drop introduced from a power source to the driver of the steering motor, and the phenomenon of steering of the wheels being hindered by a steering barrier such as a groove or a curb. 4. A steering system according to claim 2, wherein the condition codes are ranked based on the type of the phenomenon and the degree of the phenomenon. 5. The steering system of claim 4, wherein the steering controller is configured to transmit only a single status code having a higher rank even if a plurality of the status codes are transmittable. The operation controller, in the reaction force change process,
6. A steering system as claimed in claim 5, configured to change a magnitude of the actuation reaction force so that, when the status code transmitted by the steering controller is changed to raise its rank, a change amount of the actuation reaction force based on the status code before the change is added to a change amount of the actuation reaction force based on the status code after the change.

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